The present invention concerns signal-light systems, most especially those provided along roads and highways. It is known to provide emergency-phone stations at intervals along the length of a highway, the emergency-phone stations being distributed along the length of a communications cable laid along the length of such highway. Sometimes, such emergency-phone stations are provided with signal-light systems. For example, each emergency-phone station in a series of such stations may be provided with an electronic flash lamp which, from a remote central station, is caused to blink, to warn drivers that they are approaching the site of an accident, or the like. An operator at the remote central station selects which emergency-phone stations are to have their respective flash lamps blink, and the power needed to effect flashing of the flash lamps is transmitted to the activated emergency-phone stations via a power-supply line which runs along the communications cable and which supplies operating power to electrical equipment at such emergency-phone stations. The flash lamp at each such emergency-phone station is provided with a storage capacitor which serves as the power source for the respective flash lamp, with the storage capacitor being energized from the aforementioned power-supply line.
Federal Republic of Germany published allowed patent application DE-AS No. 19 33 436 discloses a blinking-light highway signalling system of this type. The moment at which the electronic flash lamp at a particular emergency-phone station will flash, and indeed each moment at which it will flash during its blinking, is determined by the instantaneous state of charge of the storage capacitor provided at that emergency-phone station. This manner of timing the flashes of the blinking action, i.e., in dependence upon the instantaneous state of charge of the associated storage capacitor, has been provided for systems in which each emergency-phone station is provided with only a single flash lamp.
However, more complicated versions of such highway blinking-light signalling systems have been sought, in which the signalling of a traffic hazard, or the like, involves a series of such emergency-phone stations, the blinking-light actions at successive ones of which are different and distinguishable from one another with respect both to the number of lamps flashing at successive stations and also with respect to the rate of blinking at different stations. For example, in the case of an upcoming traffic-accident site, a first activated emergency-phone-station blinking-light system may have only one of its flash lamps in blinking operation, the next station closer to the accident site have two of its lamps blinking, and the following station closest to the accident site having three of its lamps blinking, to provide information in the form of a subjective effect of increasing urgency, and with the rates and sequences at which the lamps at successive activated stations blink perhaps likewise differing, likewise to contribute to the subjective effect of increasing urgency.
Attempts to implement more informative signal-light actions of this kind become problematic, when reliance is to be had on conventional charge-dependent timing action, i.e., when the moment at which each flash lamp is flashed during the course of blinking action is determined by the instantaneous state of charge of an associated storage capacitor. In addition to the complexity inherent in the more complex signal-light action just described, the series of emergency-phone stations which are to be activated to provide such a multi-station blinking action will, necessarily, comprise stations located at differing distances from the remote central station from which power is supplied. Furthermore, the distance from the central station to the nearest one of the series of activated stations may be similar to that of the farthest activated stations, if the series of activated stations is far from the central station, whereas if the series of activated stations is near the central station, the distance from the central station to the farthest of these may be a multiple of the distance to the nearest of these, and so forth. All this taken together makes for a capacitive charging network which is not only complicated in configuration but whose configuration furthermore changes from one instance of use to the next.
For these reasons, the charge-dependent flash-timing action of the DE-AS No. 19 33 436 mentioned above cannot be used for so complicated and furthermore changing a capacitive charging network; mainly, the various time constants involved would change from one instance of use to another, and indeed would change even within the course of a single instance of use. This conventional approach to flash-timing action would, with the complex blinking-lamp signalling actions here in question, lead to results extending anywhere from irregular and uncontrollable interflash intervals up to total failure of some flash lamps to be fired at all, i.e., due to failure of their storage condensors to achieve an operative voltage level.
Adding somewhat to such complications is the fact that the power transmittable via the power line which will already be provided along such a succession of emergency-phone stations is low. In order to be able to transmit to the storage condensor at each such station the amount of energy needed for each flash, it is therefore not possible to employ a charging time whose duration is lower than a certain minimum. This at least tends to make the minimum interval between successive flashes at any given station incapable of being short enough to implement the quick-flash action needed to attract the attention of, or indeed even be perceivable to, the drivers of vehicles travelling at high speed along such a highway.